1. Field of the Invention
The present invention relates to a thin-film resistor having a β-phase (beta-phase) Ta (tantalum) film or an alloy film that consists mainly of β-phase Ta, a thin-film magnetic head having the thin-film resistor, a head gimbal assembly (HGA) having the thin-film magnetic head and a magnetic disk drive apparatus having the HGA.
2. Description of the Related Art
A β-phase Ta thin-film, which consists of Ta having β-phase structure, shows a rather high electric resistance (150 μΩcm to 200 μΩcm in resistivity) compared to the normal metals, and has a much less temperature coefficient of resistance of approximately 1×10−4/° C. (per degree C.), showing a much less temperature-dependent electric resistance. Therefore, the β-phase Ta thin-film is very useful as a material of thin-film resistors providing stable resistance property in wide temperature ranges. Actually, the β-phase Ta thin-film is utilized in various fields such as switching elements used for liquid crystal displays, as described, for examples, U.S. Pat. Nos. 5,442,224 and 5,654,207 and Japanese Patent Publication No. 2003-242614A. Further, Thin Solid Films vol. 275 1996 p. 203-206 describes a crystal structure of the β-phase Ta thin-film and influences of annealing to the crystal structure in detail.
Furthermore, the β-phase Ta thin-film resistor can be utilized as a means for adjusting a flying height of a thin-film magnetic head for the magnetic recording, in which the resistor is provided and generates heat due to applied currents.
The thin-film magnetic head in a magnetic disk drive apparatus hydrodynamically flies with a predetermined flying height on a rotating magnetic disk when writing and reading data signals. Recently, the flying height has a tendency to be set to a much smaller value to improve writing and reading performances. For that purpose, some techniques are proposed in which a heating means is provided in the thin-film magnetic head to control the much smaller flying height with high accuracy by positively using a thermal pole tip protrusion (TPTP) phenomenon, as described in U.S. Pat. No. 5,991,113 and US Patent Publications Nos. 2003/174430A and 2003/099054A. Here, the TPTP phenomenon is originally a behavior in which one end of the magnetic head element is protruded toward the surface of the magnetic disk due to a thermal expansion generated when write currents are applied to an electromagnetic coil element for writing.
In the case in which the β-phase Ta thin-film resistor is used as the heating means for generating the positive TPTP phenomenon, the one end of the magnetic head element can be protruded efficiently, under the condition of limiting the size of the heating means within an allowable range, because the resistor has a rather high electric resistance. Further, the much less temperature coefficient of resistance of the resistor enables a heating operation to be stably performed, especially in a constant current driving.
However, the use of the β-phase Ta thin-film resistor as the heating means in a high temperature environment is likely to cause the electric resistance property of the resistor to be varied, which has a possibility that the resistor might not work properly as the heating means and the reliability of the heating performance might be degraded.
Actually, the β-phase of Ta is a nonequilibrium phase and has a possibility of being transformed to the α-phase (an equilibrium phase) under the temperature of 400° C. (degree C.) or more. The α-phase Ta thin-film shows a much lower electric resistance (25 μΩcm to 80 μΩcm in resistivity) than the β-phase Ta thin-film, and has one or more order of magnitude larger temperature coefficient of resistance (approximately 1×10−3/° C. or more) than that of the β-phase Ta thin-film. Therefore, the β-phase Ta of the thin-film resistor used as the heating means in a high temperature environment has a possibility to be partially or totally transformed to the α-phase Ta. In some cases, the transformation to the α-phase Ta is likely to make trouble of the heating performance, that is, the degradation of the reliability as a heating means, because a required amount of heat cannot be generated in the high temperature environment.
Further, whatever an element utilizing the β-phase Ta thin-film is, an thermal treatment in the manufacturing process or a use in a high temperature environment has a possibility to cause a negative effect on the element properties. In fact, in the field of liquid crystal displays, it often becomes a problem that the thermal treatment in the manufacturing process of electrodes made of the β-phase Ta thin-film in switching elements causes a nonlinearity of the β-phase Ta to be degraded.